It is often necessary to test elements of optical networks to determine, for example, polarization mode dispersion (PMD), differential group delay (DGD), polarization-dependent loss (PDL) or other characteristics, It is known to do so by means of a polarimetric PMD analysis technique, wherein light having each of several known states of polarization is launched into the device-under-test, and the corresponding transmitted state of polarization (SOP) is then analyzed, This so-called polarimetric data is then entered into known algorithms, such as the so-called Jones Matrix Eigenanalysis (JME) method or Poincaré Sphere Analysis (PSA) method, in order to calculate the desired parameters describing the PMD-related behaviour of the test device. A key component in such a test system is a real-time Stokes analyzer to measure Stokes polarization parameters or their equivalents. Additionally, there must be a means for providing wavelength-resolved measurements, a means for launching light into the device-under-test (DUT) with several known states of polarization (SOP), and means for analyzing the SOP of the light beam leaving the DUT.
A polarimetric analysis technique disclosed by Normand Cyr, Bernard Ruchet, André Girard and Gregory W. Schinn in an article entitled “Poincaré Sphere Analysis: Application to PMD Measurement of DWDM Components and Fibers”, Proceedings of SubOptic 2001, Kyoto, Japan May 20-24, 2001 pp 571-574 uses a polarized broadband source, an SOP generator, and an element for spectrally resolving the light beam, followed by a polarimeter. Spectral resolution of the light beam can be effected using a scanning Michelson interferometer, which, when coupled with Fast-Fourier-Transform (FFT) numerical analysis, is functionally equivalent to an optical spectrum analyzer based on a more traditional grating-based scanning monochromator design. Unlike this latter design, wherein only a small spectral “slice” of the light is detected at any one time, a Michelson-interferometer-based spectrum analyzer detects the full spectrum of the light at all times, hence offering a much more efficient light-gathering capability and, consequently, a much faster measurement time.
A limitation of such a measurement technique, however, is that the Michelson interferometer itself usually exhibits undesirable PDL and a small, intrinsic PMD which limits the accuracy of the overall polarimetric PMD measurement system.